Semiconductor device including metal oxide with multiple regions

Abstract

Favorable electrical characteristics are provided to a semiconductor device, or a semiconductor device with high reliability is provided.A semiconductor device including a bottom-gate transistor with a metal oxide in a semiconductor layer includes a source region, a drain region, a first region, a second region, and a third region. The first region, the second region, and the third region are each sandwiched between the source region and the drain region along the channel length direction. The second region is sandwiched between the first region and the third region along the channel width direction, the first region and the third region each include the end portion of the metal oxide, and the length of the second region along the channel length direction is shorter than the length of the first region or the length of the third region along the channel length direction.

The invention claimed is: 
     
       1. A semiconductor device containing a metal oxide, the semiconductor device comprising:
 a gate electrode; 
 a first insulating film over the gate electrode; 
 the metal oxide over the first insulating film; 
 a pair of electrodes over the metal oxide; and 
 a second insulating film over the metal oxide, 
 wherein each of the pair of electrodes comprises a narrow region and a wide region, 
 wherein the narrow region is narrower than the metal oxide in a channel width direction, 
 wherein the wide region is wider than the metal oxide in the channel width direction, 
 wherein both the narrow region and the wide region overlap with the metal oxide, 
 wherein the metal oxide comprises a source region, a drain region, a first region, a second region, and a third region, 
 wherein the source region is in contact with one of the pair of electrodes, 
 wherein the drain region is in contact with the other of the pair of electrodes, 
 wherein the first region, the second region, and the third region are each sandwiched between the source region and the drain region along a channel length direction, 
 wherein the second region is sandwiched between the first region and the third region along the channel width direction, 
 wherein the first region and the third region each include an end portion of the metal oxide, and 
 wherein the length of the second region along the channel length direction is less than the length of the first region or the length of the third region along the channel length direction. 
 
     
     
       2. The semiconductor device according to  claim 1 ,
 wherein the length of the second region along the channel length direction is greater than 0 μm and less than 4 μm, and 
 wherein the length of the first region or the length of the third region along the channel length direction is greater than three times the length of the second region along the channel length direction and less than the length of the metal oxide along the channel length direction. 
 
     
     
       3. The semiconductor device according to  claim 1 ,
 wherein the shortest path from the source region to the drain region is included in the second region. 
 
     
     
       4. The semiconductor device according to  claim 1 ,
 wherein the metal oxide contains a first metal oxide and a second metal oxide in contact with a top surface of the first metal oxide, 
 wherein the first metal oxide and the second metal oxide each contain In, an element M (M is gallium, aluminum, silicon, boron, yttrium, tin, copper, vanadium, beryllium, titanium, iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten, or magnesium), and Zn, and 
 wherein the first metal oxide includes a region having lower crystallinity than the second metal oxide. 
 
     
     
       5. The semiconductor device according to  claim 4 , wherein the first metal oxide and the second metal oxide each include a region where an In content is greater than or equal to 40% and less than or equal to 50% of the total number of In, M, and Zn atoms, and a region where an M content is greater than or equal to 5% and less than or equal to 30% of the total number of In, M, and Zn atoms. 
     
     
       6. The semiconductor device according to  claim 4 ,
 wherein in each of the first metal oxide and the second metal oxide, the atomic ratio of M is greater than or equal to 1.5 and less than or equal to 2.5, and the atomic ratio of Zn is greater than or equal to 2 and less than or equal to 4 in the case where the atomic ratio of In is 4. 
 
     
     
       7. The semiconductor device according to  claim 4 ,
 wherein in each of the first metal oxide and the second metal oxide, the atomic ratio of M is greater than or equal to 0.5 and less than or equal to 1.5, and the atomic ratio of Zn is greater than or equal to 5 and less than or equal to 7 in the case where the atomic ratio of In is 5. 
 
     
     
       8. The semiconductor device according to  claim 4 ,
 wherein a peak at around 2θ=31° is not observed in the first metal oxide and a peak at around 2θ=31° is observed in the second metal oxide in the case where the metal oxide is measured by XRD analysis.